Commands by atoponce (57)

  • This is a simple example of using proper command nesting using $() over ``. There are a number of advantages of $() over backticks. First, they can be easily nested without escapes: program1 $(program2 $(program3 $(program4))) versus program1 `program2 \`program3 \`program4\`\`` Second, they're easier to read, then trying to decipher the difference between the backtick and the singlequote: `'. The only drawback $() suffers from is lack of total portability. If your script must be portable to the archaic Bourne shell, or old versions of the C-shell or Korn shell, then backticks are appropriate, otherwise, we should all get into the habit of $(). Your future script maintainers will thank you for producing cleaner code.


    94
    echo "The date is: $(date +%D)"
    atoponce · 2009-03-07 15:51:59 41
  • Discovering all executables on your system that can be run as another user, especially root, is critical for system security. The above command will find those files with have SUID or SGID bits set and are owned by the root user or group.


    3
    sudo find / -type f \( -perm /4000 -a -user root \) -ls -o \( -perm /2000 -a -group root \) -ls
    atoponce · 2009-03-02 18:48:17 14
  • Rather than typing out all 10 files, you can use brace expansion to do the trick for you. This is useful for backup files, numbered files, or any files with a repeating pattern. Gives more control than 'rm file*' as I might want to keep others around.


    4
    rm file{1..10}
    atoponce · 2009-03-02 14:42:05 170
  • When downloading RPMs from the Internet, you don't have to 'rpm -i' or 'rpm -U' to install the package. Especially, if the package has dependencies. If you have YUM setup to access an RPM repository, this command will install the downloaded package, then any dependencies through YUM that it relies on. Very handy on RPM-based systems.


    6
    yum localinstall /path/to/package.rpm
    atoponce · 2009-03-02 14:32:23 8
  • In this case, I'm keeping an eye on /var/log/messages, but of course any file will do. When I'm following a file, I generally don't want to see anything other than what has been added due to the command or service I've executed. This keeps everything clean and tidy for troubleshooting.


    3
    tail -n 0 -f /var/log/messages
    atoponce · 2009-03-02 14:21:18 11
  • This is a simple case of recursing through all directories, adding the '.bak' extension to every file. Of course, the 'cp $file $file.bak' could be any code you need to apply to your recursion, including tests, other functions, creating variables, doing math, etc. Simple and clean recursion.


    1
    find . -type f | while read file; do cp $file ${file}.bak; done
    atoponce · 2009-03-01 23:42:49 16
  • Useful mainly for debugging or troubleshooting an application or system, such as X11, Apache, Bind, DHCP and others. Another useful switch that can be combined with -mmin, -mtime and so forth is -daystart. For example, to find files that were modified in the /etc directory only yesterday: sudo find /etc -daystart -mtime 1 -type f


    34
    sudo find / -mmin 60 -type f
    atoponce · 2009-03-01 23:03:31 16
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Numerically sorted human readable disk usage
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Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Retry the previous command until it exits successfully

Split huge file into DVD+R size chunks for burning
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Find the package that installed a command

Delete all but the latest 5 files, ignoring directories

cat stdout of multiple commands
Concatenate the stdout of multiple commands.

Generates a TV noise alike output in the terminal
Generates a TV noise alike output in the terminal. Can be combined with https://www.commandlinefu.com/commands/view/9728/make-some-powerful-pink-noise

check open ports without netstat or lsof

Check command history, but avoid running it
!whatever will search your command history and execute the first command that matches 'whatever'. If you don't feel safe doing this put :p on the end to print without executing. Recommended when running as superuser.


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